Canterbury water could be 'undrinkable' in 100 years because of nitrates

Saturday, 22 June 2019

Christchurch’s pristine water is world renowned and safe to drink straight from the tap. But will this statement ring true in 50 or 100 years?

Users of Canterbury's world-renowned drinking water have been issued a dire warning: 'Pollution could render it undrinkable in 100 years.'

The warning comes from the Canterbury Medical Officer of Health, Dr Alistair Humphrey, as concern builds over nitrates entering the water supply from dairy farms.

In the latest publicly-funded Frank Film episode – Dairy farming and the water we drink – Humphrey warns of the risk of nitrate contamination in Christchurch's water.

Canterbury Medical Officer of Health Alistair Humphrey has issued a warning about drinking water for the future, but stressed that it is safe to drink now.

He has assured residents their drinking water is currently safe to consume. His fear is for the future, and a predicted nitrate influx.

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Dr Humphrey would like to see fewer cows on Canterbury pastures.

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'Modelling from Environment Canterbury shows that nitrates on the north side of the Waimakariri River are flowing underneath that river toward the Christchurch urban drinking water supply,' Humphrey said.

'Scientists say there is a 75 per cent chance that nitrate levels will increase significantly in the urban water supply in the next century.'

Christchurch's alpine-fed, aquifer-purified water system is unique in New Zealand and, according to river engineer Rob Blakely, there are few systems like it in the world.

'The fact that it comes out of the mountains, the snow covered mountains, and it flows across these wonderful plains with lots and lots of layers of gravel, hundreds if not thousands of feet deep,' Blakely said.

'When we draw water out of the aquifers of this river we're getting the most beautiful, pristine water you could ever imagine. We need to be very careful that the water flowing into this river system is kept clean.'

The region now has 1.3 million dairy cattle grazing the Canterbury plains.

'Nitrogen is applied to improve poor quality soils,' Humphrey said.

'Cows excrete nitrogen as nitrate onto the paddock and into our aquifers.'

He warned that nitrates are already showing up in shallow, private bores throughout Canterbury, some at levels above the World Health Organisation's maximum allowable value of 11.3mg per litre.

Water filter retailer Sue Kelly said reverse osmosis filters, imported from the United States and costing more than $1200, remove nitrates from drinking water. Hundreds of the under-bench units have been sold, and since a Danish study was released public awareness has grown further.

The study, of 2.7 million people, found a link between nitrates in drinking water and bowel cancer.

Humphrey has scrutinised the research and said 'the study accounted for all those other variables that may also give rise to bowel cancer, nonetheless it showed that nitrates in drinking water are a considerable contributor to this deadly and debilitating disease'.

He wanted the study replicated in New Zealand.

He also wanted a concerted effort to reduce cow numbers in Canterbury.

* Frank Film – Changing South is funded by NZ on Air to produce South Island stories. For more Frank stories, visit www.frankfilm.co.nz Comments on this story are now closed